1) Field of the Invention
The present invention relates to a technology for coupling a shaft to another shaft.
2) Description of the Related Art
In image formation apparatuses, it is required to rotate with high-precision a photosensitive member (a rotating member) carrying an image to obtain images of high-quality. In particular, rotation of high-precision is important in the tandem type full color image formation apparatus. The tandem type full color image formation apparatus includes a plurality of photosensitive members each onto which an image of a different color is formed. Each of the images formed on the photosensitive members are then transferred onto an intermediate transfer belt or a transfer sheet directly with the images being superimposed onto one another to obtain a full color image. Therefore, the rotation of high-precision is required to prevent the full color image from being out of color registration.
A motor of high-precision may be used to improve the precision of rotation of the rotating member in the tandem type full color image formation apparatus. However, even if the motor of high-precision is used, if the central axes of the rotating shaft of the motor and the shaft supporting the photosensitive member are displaced from each other at a position in which the shafts are coupled, the rotation of the photosensitive member becomes non-uniform. As a result, deterioration in image quality caused by unevenness of the image called banding or a positional deviation in a sub-scanning direction of the photosensitive member on the surface of the photosensitive member is caused.
A conventional shaft coupling device for coupling a rotating shaft supporting -a photosensitive member and a shaft of a motor rotating the rotating shaft is described in a Japanese Patent Application Laid-Open No. 2002-357986 (see page 4 and FIGS. 7 to 9). A motor is fixed to an image formation apparatus by the shaft coupling device. That is, a flange is attached to the rotating shaft of the photosensitive body. A drum coupling unit having a notch is attached to the shaft of the motor. A spring pin is fixed to the rotating shaft such that the spring pin protrudes from the rotating shaft in a radial direction of the rotating shaft. The flange is fitted with the drum coupling unit and the spring pin with the notch of the drum coupling unit. Screws are then inserted into four holes provided on the motor to fix the motor to the image formation apparatus.
According to the shaft coupling device, the rotating shaft of the photosensitive member and the shaft of the motor are coupled to each other by fitting of the spring pin attached to the rotating shaft into the notch of the drum coupling unit. In other words, the coupling between the shafts is not highly precise because the rotating shaft of the photosensitive member and the shaft of the motor are not completely integrated with each other. Consequently, there is a possibility that the central axes of the coupled shafts may be displaced from each other.